Note: PTFE is the generic name for what people often refer to as Teflon®. Genuine Teflon® is a registered trademark of the DuPont Corporation. Most of the slide bearing assemblies that The Steel Supply Company provides are made with Fluorogold®, which is a PTFE and Fiberglass composite. Fluorogold® is a registered trademark of the Saint-Gobain Corporation.
There are several factors that control the lifespan of a slide bearing assembly. Among them are; Composition of the Teflon®, Fluorogold® or PTFE; The strength of the bond; Is the assembly exposed to exterior environment conditions; The load the slide bearing is carrying; The amount and frequency of movement, etc.
Addressing each condition in order:
Slide bearings made with pure Teflon® or PTFE will not show the same durability as Fluorogold®. The difference derives from the composition of each product. Pure Teflon®, often referred to as “Virgin Teflon®”, is not designed for abrasive conditions. Fluorogold® could be referred to as a PTFE derivative. It is produced by infusing PTFE with fiberglass reinforcing fibers. The result is greater dimensional stability and greater abrasion resistance.
The bond between the steel backing plate and the Teflon®, Fluorogold® or PTFE is also critical to the longevity of the bearing. In some cases, the bearing is intended to last the entire life of the structure so the process used to bond the two is critical. The standard procedure is to etch the Fluorogold®,apply the epoxy and lay the Fluorogold on the steel back plate. The stock slide bearing is made in 24” x 48” sheets, so a specially designed clamp applies pressure evenly from both the top and bottom across the entire 8 square foot surface.
It is essential that the surfaces remain flat. The assembly, including the clamp, is then placed in an pven and brought up to 450°F. This allows a complete, permanent bond between the steel and Teflon that will provide maximum durability.
The question of interior or exterior location is probably the most important factor in the lifespan of the slide bearing. In interior applications, shielded from moisture, temperature extremes and debris often they will last the life of the structure. However, exterior environments are a completely different story. Any debris on the surface will cause abrasion that will wear away the Fluorogold®. Manufacturing the upper element to be larger than the lower is an important part in limiting the debris issue.
The real enemy of the exterior slide bearing is rust. If the steel backing plate is allowed to rust that will eventually spread until it corrodes the steel surface the Fluorogold is bonded to. That will destroy the epoxy bond and the Fluorogold with begin to disintegrate when movement occurs. Rust can be controlled several ways. The steel backing plate can be made of stainless steel, it can be carbon steel that is hot dip galvanized, or the steel backing plate can be painted with a DTM (Direct to Metal) primer. If it is painted, it should be recoated as needed.
Load and Frequency are fundamental factors in Slide Bearing longevity. The greater the pressure on the bearing surfaces, the more friction created when movement occurs. As well, the more often movement occurs the more wear the slide surfaces will exhibit. Engineers will limit these two factors in the design of the Slide Bearing. The standard design has a load limit of 2,000 psi. The dimensions of the lower element determine the surface area, so for example;
Lower Element with dimension 8” x 6” = 48 sq. in. x 2,000 psi = 96,000 lbs. of load capacity.
If the engineer felt the pressure on this bearing would cause it to wear prematurely he would increase the dimensions hence the load capacity, or he would disperse the load over a larger number of Slide Bearing assemblies.
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